SaO2: Definition, Oxygen Saturation, Normal Levels and Oxygen Level Measurement

It measures the percentage of how much hemoglobin is saturated with oxygen.

The abbreviation “SaO2” refers to oxygen saturation.

Oxygen is transported in the blood in two ways: oxygen dissolves in blood plasma (partial pressure of oxygen, pO2) and oxygen bound to hemoglobin (SaO2).

About 97% of oxygen is bound to hemoglobin, while 3% dissolves in plasma.

Oxygen saturation (SaO2) and oxygen partial pressure (pO2) have direct relationships; if one decreases, as does the other.

The relationship between oxygen saturation (SaO2) and partial pressure oxygen (PaO2) is known as the oxyhemoglobin (HbO2) dissociation curve.

Oxygen saturation (SaO2) of about 90% is associated with partial pressure oxygen (PaO2) of about 60 mmHg.


Understanding oxygen saturation

Oxygen saturation, sometimes known as O sats or simply sats, refers to how hemoglobin is saturated with oxygen.

Hemoglobin is an element in the blood that binds with oxygen to transport it through the bloodstream to the body’s organs, tissues, and cells. Normal oxygen saturation is usually between 96 percent and 98 percent.

Each of our red blood cells contains four molecules of hemoglobin.

Iron, which is present in hemoglobin, is what oxygen binds to after diffusing from the alveoli in the lungs and into the capillaries in the lungs. Most of the time, hemoglobin is entirely saturated.

The oxygen saturation depends on:

  • Oxygen availability.
  • Gas exchange in the lungs: the ability of oxygen to reach the alveoli and, once in the alveoli, diffuse through the walls of the alveoli and capillaries to get the red blood cells.
  • The concentration of hemoglobin in red blood cells.
  • The affinity of hemoglobin for oxygen, in other words, the force with which hemoglobin attracts oxygen.

Measurement of oxygen saturation

Oxygen saturation is most commonly measured by:

Arterial blood gases: The value obtained from arterial blood gases or ABG (SaO2) describes the oxygen saturation of the arterial blood and is accepted by drawing blood from an artery such as the radial artery in the wrist or the femoral artery in the groin.

Pulse Oximetry: The value obtained from peripheral capillary blood using pulse oximetry (SpO2) often reflects the levels found in arterial blood.

Pulse oximetry has the advantage of being a non-invasive test, using a probe attached to a finger or ear, or other regions of the body that reads the wavelengths of light reflected from the blood.

Not only are pulse oximeters a standard now for monitoring people in the hospital, but they can also even track their saturation through wearable technology.

Decreased oxygen saturation

A drop in oxygen saturation levels refers to desaturation or hypoxemia and can be caused by any change or damage in the above variables.

A change in oxygen availability can be caused by decreased oxygen concentration in inspired air, such as at higher altitudes and when flying in an airplane.

Problems with a gas exchange that cause a decrease in oxygen saturation can include anything that reduces the ability of oxygen to travel from the outside air into the alveoli of our bodies or when transferring oxygen from the alveoli to the capillaries of the blood.

The decrease in oxygen saturation may be due to a lower hemoglobin concentration, as in iron deficiency anemia.

A decreased affinity of hemoglobin for oxygen can occur when something else is present that binds more strongly to hemoglobin than oxygen, as in carbon monoxide poisoning in which the compound carboxyhemoglobin is formed.

Hypoxemia and hypoxia

The terms hypoxemia and hypoxia are often used interchangeably, but they mean very different things. Hypoxemia is the term that defines a decrease in the concentration of oxygen in the blood.

Hypoxia, in turn, describes the consequences that occur due to hypoxemia. When cells don’t get enough oxygen, they can adapt if the deficiency is slight.

However, in the most significant deficiencies, the result is cell damage followed by cell death.

Hypoxia is often caused by hypoxemia but can also occur when:

  • There is anemia because there are too few red blood cells, so even fully oxygenated blood does not bring enough oxygen to the tissues.
  • Blood flow is inadequate, so even fully oxygenated blood does not reach the tissues.
  • The tissues are incapable of the well-oxygenated blood that is delivered.
  • The tissues require even more oxygenated blood than can be given, as in severe infections.

Treatment of hypoxemia and hypoxia due to hypoxemia

When oxygen saturation falls below a certain level, supplemental oxygen therapy is usually needed, sometimes on an emergency basis.

It is also essential to determine the cause of low oxygen saturation. Treatment of the underlying cause is the primary goal of treatment.

What should my oxygen saturation level be?

A range of 94-99% is expected for healthy adults breathing room air that contains 21% oxygen.

Anyone not reaching the critical blood oxygen saturation level of 90% (SpO2, peripheral capillary oxygen saturation) or 55-60mmHg (SaO2, arterial oxygen saturation) may require additional oxygen.

A qualified physician will assess your situation and prescribe the appropriate dose of supplemental oxygen.

Oxygen saturation levels: what do they mean?

Oxygen saturation levels measure the degree to which hemoglobin contained in red blood cells ( erythrocytes ) has bound to oxygen molecules. Oxygen is absorbed by the lungs when we breathe.

The two most common ways to assess blood oxygen saturation are arterial blood gases and pulsatile oxygen.

What does an arterial blood gas measure?

An arterial blood gas test measures how efficiently your lungs carry oxygen into the bloodstream and remove carbon dioxide. The arterial blood gases are taken from an artery, usually in the wrist.

This procedure can be a bit painful. The critical oxygen level in the blood is 55-60 mmHg (SaO2, arterial oxygen saturation), with readings below this level indicating that the person is not hydrogenated.

What does a pulse oximeter measure?

A pulse oximeter indirectly measures oxygen saturation levels.

This non-invasive process involves inserting a finger (it can also be used in the ear or toe) into the device, where a red light calculates the redness of the blood by pulsing through the finger.

The pulse oximeter measures hemoglobin by providing a mean saturation percentage (SpO2, peripheral capillary oxygen saturation).

The critical level is considered a peripheral capillary oxygen saturation (SpO2) of 90% (equivalent to an arterial oxygen saturation of 55-60 mmHg).

The underlying principle of the oximeter is that it measures the redness of the blood: the redder, the higher the oxygen saturation.

Living with lung diseases like chronic obstructive pulmonary disease (COPD), emphysema, and pulmonary fibrosis can struggle.

However, you can live a quality, enjoyable life by following a simple daily routine that includes good self-care.

If you need medical oxygen, there are portable and stationary systems to meet your oxygen needs that can minimize the inconvenience associated with oxygen therapy.

The oximeter can be used as a biofeedback training device in conjunction with pursed-lip breathing to increase the oxygen level.

Your need for oxygen

Your need for oxygen is continuous; the human body needs oxygen, food, and water to create energy and fuel our active life. Oxygen must be brought in from the outside air and transported to each cell every minute.

This is a continuous route of transport systems; your lungs supply oxygen to your bloodstream, your heart pumps blood to tissues, or oxygen is given to each cell.

Each cell has a manufacturing system called mitochondria, which uses oxygen and food to create energy for the muscles to power the body; carbon dioxide, the waste product of this process, is expelled.

Every tissue in your body constantly requires oxygen to create the energy of life.

There is a lot of oxygen in the atmosphere to meet the needs of people with normal lungs.

However, you may need extra oxygen to meet your body’s oxygen requirements if you have lung disease. You may have been diagnosed with chronic obstructive pulmonary disease or pulmonary fibrosis.

Chronic obstructive pulmonary disease combines bronchitis, asthma, and emphysema, while pulmonary fibrosis is the accumulation of scar tissue that prevents oxygen transfer across the alveolar-capillary membrane.

Determine your oxygen need

Your doctor will prescribe oxygen based on the oxygen level in your bloodstream during rest, exertion, and sleep.

Oximetry is the most convenient method of evaluating your oxygen level.

Your oximeter tells you how much of your blood is filled with oxygen. Your pulse oximetry reading is essential information, but it is not isolated; combined with other information, you and your doctor can make important decisions to guide your self-monitoring program.

How your body picks up oxygen

The diaphragm pulls down, and the chest muscles are stretched to elongate and widen the chest to allow room for air to enter the lungs.

Oxygen in the air reaches the expanding alveoli or air pockets where the network of tiny blood vessels called capillaries receives oxygen as it diffuses through the alveolar-capillary membrane.

At the same time, carbon dioxide is produced in the body’s cells and transported in the hemoglobin molecule.

Red blood cells are shed and deactivated through the capillary membrane of the alveoli to be exhaled through the atmosphere.

Once in the blood, oxygen quickly attaches itself to the hemoglobin molecule in the red blood cell, turning it red.

The freshly oxygenated blood is pumped by the heart through the main arteries to the vital organs, muscles, and others; it comes to supply oxygen to every one of the cells once inside the cell, and the oxygen finds its way to the mitochondria that use oxygen to create energy.

Carbon dioxide, the end product of the body’s metabolism, is carried through the bloodstream to the lungs. It is exhaled into the atmosphere, thus completing one of the millions of life-sustaining cycles.

Measuring your oxygen level

As your red blood cells gather oxygen into the hemoglobin molecule, they turn red. Oximetry is based on the redness of the blood; as the blood’s ability to hold oxygen fills up, the blood becomes redder.

The oximeter functions by illuminating two lights, red and infrared, through your finger, the sensors on the other side of your finger detect the amount of light passing through.

Red light measures non-oxygenated hemoglobin, while infrared light measures oxygenated hemoglobin.

A small computer inside the oximeter compares the two lights and displays a number that indicates what percentage of hemoglobin is saturated with oxygen.

The oximeter is designed to take its reading at the peak of the pulse, where the blood contains the most oxygen. There is less oxygenated blood at any other point in the beating, causing an incorrect reading.

So it is imperative to make sure the oximeter is detecting regular pulses; now, most oximeters have a display or pulse indicator that informs you of periodic pulses.

The average oxygen level is about ninety-five to ninety-seven percent at sea level, but ninety percent is barely acceptable.

Oximeter compared to arterial blood gases.

Arterial blood gases measure your oxygen saturation level by drawing blood from your artery.

It is the most accurate measure of your oxygen saturation level, and it also measures your carbon dioxide and provides other helpful information.

On the downside, it is invasive and involves a needle stick, and measures only one point in time. Oximetry measures only oxygen, but it does so non-invasively and continuously.

It is non-invasive and inexpensive during exercise and sleep, patients can use it at home or anywhere, and patients can use it to learn how to increase their oxygen level.

Put the throttle clip on your finger, hold it steady, wait for the pulse to stay stable and the pulse oximetry steady, then take your reading.

Avoid dark nail polish or artificial nails, do not pinch the head as it may cut off circulation to your finger.

Avoid excessive movement of your finger that could give a false reading; here are some suggestions, if the pulse is per week, try running warm water from your hand to increase blood flow or relocate the oximeter; during exercise, try to relax your hand to maximize blood flow.

The critical point is that there is a lag time for any change in the oxygen in your blood to reach your finger. So be sure to wait twenty to thirty seconds before taking your last reading.

Oximetry during exercise

If you have lung disease, daily exercise, such as walking, is an integral part of maintaining your health.

Exercise is essential for active living; whether you exercise or move around to increase your body’s metabolism, you need more oxygen when you are busy.

Your doctor will determine your oxygen need during exercise; your oximeter will inform you if your oxygen level is adequate during exercise or activity.

Body movements can cause false oximetry readings when exercising, so keep your finger steady when taking the task, and make sure the oximeter shows a solid and regular pulse.

Exercising the body requires more oxygen.

Your oxygen level may drop when you increase your activity, so your resting oxygen setting may be inadequate to meet your body’s needs during exercise. The drop in saturation may be why you had to stop exercising.

To detect the lowest oxygen level, keep reading the oximeter for about thirty seconds after you stop exercising; the saturation may continue to drop.

Report low oxygen readings to your physician and provide instructions for adjusting the oxygen settings during exercise. It is essential that you can maintain adequate oxygen levels during exercise.

Airplanes are pressurized to 5,000 to 8,000 feet and sometimes higher, not sea level; this is equivalent to the Denver attitude.

If you need oxygen on the ground, you will need oxygen during the flight (sometimes you don’t).

But if you need it during the air flight, your doctor will make that decision, be sure to plan your trip for at least two to three weeks and inform the airline that you will need oxygen; each airline has its own set of procedures for oxygen.

You can buy oxygen from the airline. However, it is best to use a portable oxygen concentrator from your oxygen supplier.

Your doctor will write you a prescription for oxygen; one copy will go to the airline and another to your oxygen company. In-flight, your oximeter will tell you if the oxygen setting is adequate.

In pulmonary rehab, we teach a breathing technique called pursed-lip breathing that can increase your oxygen level; breathe in through your nose, and breathe out slowly through your mouth while pursing your lips.

Think of it this way, smell the roses and gently blow out the candle making the flame flicker through your nose and pursed lips.

Using your oximeter as a guide for pursed-lip breathing, you can learn to raise your oxygen level by three or four points.

Just focus on the oximeter while breathing with pursed lips; if you are successful, your oxygen level will increase. Pursed lips that live with oximetry are especially helpful when active and exercising.

It is important to remember that it takes time for blood to travel from your lungs to your finger oximeter. So wait about twenty seconds to determine if there is a change in your oximetry reading. Being persistent, practice makes perfect.

Control over your lung disease is determined by managing it at home, taking your medication and oxygen properly, keeping your airways clear, exercising, and monitoring for an infection or outbreak of your disease.

We all make a big difference in how your lung disease affects you. When there is any change in your condition, you must call your doctor.

Some doctors give their patients an immediate action plan to start in case of signs or symptoms of an infection; the characteristics are:

More shortness of breath, coughing up sputum, and a change in your oximetry reading may indicate an infection, a flare at the time you may need antibiotics, prednisolone, and inhalers as a change in your oxygen settings.

This will be determined and prescribed by your doctor.

You need to obtain a quality oximeter and use it correctly; your oxygen needs are higher when you are active, exercising at higher altitudes, or on an airplane.

Therefore, you should monitor your oximetry during each of these conditions; a change in your oximetry level may indicate a difference in your state or even a flare and the need to call your doctor.

Practice your oximeter lip breathing bag as a guide to increasing your oxygen level. Use your oximeter in good health and as directed by your physician.